Aluminum base alloys

ABSTRACT

Wrought aluminum base alloys having high strength and improved toughness. The alloys consist essentially of zinc from 4 to 9 percent, magnesium from 1 to 4 percent, zirconium from 0.05 to 0.40 percent, copper from 0.5 to 3.5 percent, boron from 0.01 to 0.05 percent and the balance essentially aluminum.

Unitefi States Patent 1 [111 3,762,916

Kirman Oct. 2, 1973 ALUMINUM BASE ALLOYS [75] Inventor: Ivor Kirman, Birmingham, England [56] References Cited) [73] Assignee: Olin Corporation, New Haven, UNITED STATES PATENTS Conn 3,198,676 8/1965 Sprowls et al. l48/l59 [22} Filed: July 1972 Primary Examiner-Richard 0. Dean 21 APPL No 270 254 Attorney-Robert H. Bachman Related U-S. Application Data [63] Cipntijnuattilon-in-partofSer.No.42,48l,June 1,1970, wrought aluminum base alloys having high Strength a an one and improved toughness. The alloys consist essentially of zinc from 4 to 9 percent, magnesium from 1 to 4 per- [52] Cl 75/141 148/127 cent, zirconium from 0.05 to 0.40 percent, copper from Int Cl czzc 21/00 0.5 to 3.5 percent, boron from 0.01 to 0.05 percent and 58 Field of Search 75/141, 146; 148/32, the balance essem'any alummum' ALUMINUM BASE ALLOYS CROSS REFERENCE TO RELATED APPLICATION This case is a continuation-impart of copending application Ser. No. 42,481 by Ivor Kirman for Aluminum Base Alloys, filed June 1, 1970, now abandoned.

BACKGROUND OF THE INVENTION However, such alloys generally have low'toughness in the aged condition.

It is also known to provide critical processing conditions in order to improve the toughness in the aged condition; however, obviously this adds to manufacturing costs. In addition, conventional processing order to improve the toughness in the aged condition frequently does so by sacrificing strength.

It is, therefore, highly desirable to provide a family of heat treatable aluminum base alloys which overcome the foregoing disadvantages.

It is, therefore, an object of the present invention to provide a familyof heat treatable aluminum base alloys with improved toughness, which alloys contain zinc, magnesium and copper.

It is a further object of the present invention to provide alloys as aforesaid which have high strength characteristics.

It is a further object of the present invention to provide alloys as aforesaid which have high strength and improved toughness in the heat treated and aged condition without the necessity of complicated and expensive processing.

Further objects and advantages of the present invention will appear from the ensuing discussion.

SUMMARY OF THE INVENTION In accordance with the present invention it has now been found that the foregoing objects and advantages may be readily obtained.

The wrought aluminum base alloy of the present invention consists essentially of zinc from 4 to 9%, magnesium from 1 to 4%, zirconium from 0.05 to 0.40%, copper from 0.5 to 3.5%, boron from 0.01 to 0.05%, and the balance essentially aluminum. The alloy of the present invention has high strength and improved toughness in the heat treated and aged condition. It is a surprising finding of the present invention that the zirconium plus boron addition in the copper-containing alloys of the present invention enables the attainment of high strength plus improved toughness in the heat treated and aged condition.

DETAILED DESCRIPTION It has been found that the alloy of the present invention has severaladvantages. The alloy of the present in vention is characterized by having surprisingly improved toughness in the heat treated and aged condition. This is an important property which is also known as resistance to tearing and is a measure of resistance to fracture or rapid propagation of cracks in articles under stress. This property can be measured for comparative purposes by the Kahn-Type Notched Tear Test as described by J. G. Kaufman and A. H. Knoll, Materials Research And Standards, April 1964, pages 151 to 155.

It is a significant advantage of the present invention that this surprisingly improved toughness in the heat treatable and aged condition is obtainable with no critical or special processing requirements. In addition, the surprising toughness of the alloys of the present invention are combined with high strength properties. For example, the alloys of the present invention may be readily age hardened to yield strengths in excess of 70,000 psi.

Furthermore, the surprising properties of the alloys of the present invention are obtained without the necessity for the addition of chromium which is conventionally added to improve resistance to stress corrosion cracking but generally results in low toughness in the aged condition. Naturally, chromium may be added in small amounts if desired to obtain particular properties, for example, chromium is preferably used with a 0.05 percent max. Chromium additions in excess of 0.1 percent result in the precipitation of chromium-rich phases which are injurious to toughness. Hence, it is preferred that the alloys of the present invention be substantially chromium free.

In accordance with the present invention, the toughness of the foregoing wrought aluminum base alloys in the heat treated and aged condition is surprisingly improved by alloying with zirconium and boron in the foregoing ranges. It is particularly surprising that this combination of zirconium and boron is so effective since boron is not normally expected to have such an effect, i.e., it is normally utilized in small amounts to produce a fine grain size in the cast form.

In accordance with the present invention, the alloy consists essentially of zinc, magnesium, copper, zirconium and boron in the foregoing ranges. Thus, zinc should be present in an amount from 4 to 9 percent and preferably from 5.0 to 6.5 percent. Magnesium should be present in an amount from 1.0 to 4.0 percent and preferably from 2.0 to 3.0 percent. Zirconium should be present in an amount from 0.05 to 0.40 percent and preferably from 0.1 to 0.2 percent. Copper should be present in an amount from 0.5 to 3 .5 percent and preferably from 1 to 3 percent. Boron should be present in an amount from 0.01 to 0.05 percent and preferably from 0.01 to 0.02 percent. In accordance with the present invention all percentages listed in the present specification are weight percentages.

Copper is a particularly important alloying ingredient since the effect of the zirconium plus boron addition is of greatest significance with the copper addition. In fact, the major improvements of the present invention are not obtained in the copper-free alloys. The zirconium plus boron additions of the present invention to copper-free alloys do achieve high strength without critical or special processing requirements; however, they do not attain the surprisingly improved toughness of the copper-containing alloys of the present invention. It has been foundin accordance with the present invention that the instant copper-containing alloys fracture transgranularly so that the zirconium plus boron additions markedly improve the toughness; whereas, the copper-free alloys fracture intergranularly so that the zirconium plus boron additions do not have this effect.

Naturally, the alloys of the present invention may contain other additives which are utilized in order to obtain particular properties or particular results and may also contain impurities which are common to alloys of this type. Thus, titanium may be present in an amount from to 0.1 percent and preferably up to 0.05 percent max., manganese from 0 to 0.2 percent and preferably up to 0.1 percent max., silicon up to 0.4 percent max., and iron up to 0.5 percent max. High titanium levels should be avoided, similar to chromium, because titanium-rich phases impair toughness. It is preferable to restrict the total iron plus silicon level to less than 0.4 percent in order to insure the attainment of high toughness.

The alloys may be processed in a conventional manner. Thus, the alloys may be cast, homogenized and hot and cold rolled in a manner typical for alloys of this type.

Following the foregoing, the alloys of the present invention are heat treated and aged in order to achieve their high strength and improve toughness. The solution heat treatment involves heating them to a temperature within the range of 750 to 1,000F and holding at that temperature range for at least minutes for a period of time sufficient to obtain substantially complete solution of the zinc and magnesium components and also the copper component. Periods of time of from 5 minutes to 48 hours are conventionally used.

At the conclusion of the solution heat treatment, the material should be rapidly cooled as by quenching to substantially room temperature in order to retain a substantial portion of the dissolved elements in solution in the alloys.

The material is then aged by holding at a temperature Aging treatment 0.2% yield stress Unit propagation ksi energy in lb/in' 24 Hours at 250F 81.0 600 t 100 Hours at 300F 75.0 450 t 100 5 1 Hour at 350F 69.0 750 i 100 EXAMPLE [1 For comparison, Alloy 2 containing chromium was 10 cast with the following composition:

Zn Mg Cu Fe Si Cr 5.6% 2.5% 1.6% 0.1 0.015% 0.30%

The alloy having the foregoing composition was cast 5 from 1300F and processed to 0.065 inch by the same schedule as the above alloy.

Aging Treatment 0.2% yield stress Unit propagation ksi energy in lb/in' 24 Hours at 250F 77.0 350 i 100 EXAMPLE I11 Alloy composi 2 tion Zn Mg Cu I Fe Si Zr 7 B 5.6% 2.5% 1.7% 0.11% 0.015% 0.12% 0.02% Alloy 3 having the foregoing composition was cast from 1,400F and processed according to the same schedule as Example 1.

Aging treatment 0.2% yield stress Unit propagation ksi energy in lb/in 24 Hours at 250F 78.0 900 i 100 of from 200 to 400F for from 30 minutes to 48 hours. 3

Alloys having the compositions identified in Table 1 below were prepared in a manner after Example I. The aging treatment was 24 hours at 250F. Properties are given in Table 11 below. i

TABLE I Casting tem- Alloy Zn Mg Cu Fe Si Other elements perature, "F

4 5.6 2.5 1.6 0.3% Cr 1300 5 5.62 2.48 1.57 0.062 0.02 1300 6 5.48 2.45 1.72 0.108 0.015 0.2% Zr 1400 7 5.48 2.45 1.72 0.108 0.015 0.2% Zr+0.02%B 1400 8 5.48 2.45 1.72 0.108 0.015 0.l%Zr+0.0l%B 1300 9 5.6 2.5 1.6 0.3% Zr+0.02% B 1475 .10 5.48 2.45 1.72 0.108 0.015 0.49% Ti 1300 11 5.35 2.59 0.10 0.11 0.030 0.20% Zr 1400 12 5.36 2.67 0.10 0.11 0.030 0.20% Zr+0.01%B 1400 Naturally, more complex aging treatments may be TABLE 11 used, if desired. 0 1d Alloy .2 0 yie Unit propagation The present invention and improvements result ng stressyksi UTSkSi Em) energy'inlbfin, therefrom will be more readily apparent from a consid- 3 6 ration 0 follow 4 4 e f the mg illustrative examples 5 66.0 75.0 90 560 6 81.0 91.5 10.5 620 EXAMPLE I 7 77.5 86.0 11.0 850 A s 69.0 80.5 12.0 890 gg 9 86.0 94.0 9.5 500 tion: Zn Mg Cu 0 Fe Si Zr g 5.6% 2.5% 1.7% 0.11% 0.015% 0.2% no 781 100 180 The alloy having the foregoing composition, identified This invention may be embodied in other forms or as Allo was cast from into a 2,000 m D carried out in other wa s without de artin from the Y 8 y P g ville ingot. The ingot was homogenized for 24 hours at. spirit or essential characteristics thereof. The present 865F with 50F/hour heating up and cooling down embodiment is therefore to be considered as in all re- It was b eq n y hot rolled at 700F i I0 spects illustrative and not restrictive, the scope of the 0.200 inch thickness and cold rolled to 0.062 inch. Test specimens were solution treated for one hour at 900F, water quenched and aged.

invention being indicated by the appended claims, and all changes which come within the meaning and range 9? ii e sns 1 13 09 fifii th t What is claimed is:

1. A wrought aluminum base alloy having improved toughness and high strength consisting essentially of zinc from 4 to 9 percent, magnesium from 1 to 4 percent, zirconium from 0.05 to 0.40 percent, copper from 0.5 to 3.5 percent, boron from 0.01 to 0.05 percent and the balance essentially aluminum.

2. An alloy according to claim 1 wherein said alloy is substantially chromium free.

3. A wrought aluminum base alloy having improved toughness and high strength consisting essentially of zinc from 4 to 9 percent, magnesium from 1 to 4 percent, copper from 0.5 to 3.5 percent, zirconium from 0.05 to 0.40 percent, boron from 0.01 to 0.05 percent and the balance essentially aluminum, said alloy being in the heat treated and aged condition and having high strength and improved toughness.

4. An alloy according to claim 3 wherein the zinc is present in an amount from to 6.5 percent.

5. An alloy according to claim 3 wherein the magnesium is present in an amount from 2 to 3 percent.

6. An alloy according to claim 3 wherein the zirconium is present in an amount from 0.1 to 0.2 percent.

7. An alloy according to claim 3 wherein the boron is present in an amount from 0.01 to 0.02 percent.

8. An alloy according to claim 3 wherein the copper is present in an amount from 1 to 3 percent.

9. An alloy according to claim 3 containing titanium up to 0.1% max., manganese up to 0.2 percent max., silicon up to 0.4% max., and iron up to 0.5% max.

10. An alloy according to claim 3 wherein said alloy is substantially chromium free.

111. A process for providing improved toughness and high strength in a wrought aluminum base alloy consisting essentially of zinc from 4 to 9 percent, magnesium from 1 to 4 percent, zirconium from 0.05 to 0.40 percent, copper from 0.5 to 3.5 percent, boron from 0.01 to 0.05 percent, balance essentially aluminum, which comprises:

A. hot rolling said alloy;

B. cold rolling said alloy;

C. solution heat treating said alloy at a temperature of from 750 to l ,000F for at least 5 minutes fol.- lowed by rapid cooling; and

D. aging for at least 30 minutes at a temperature of from 200 to 400F.

12. A process according to claim 11 wherein said magnesium, zinc and copper components are substantially retained in solution following said rapid cooling.

13. A process according to claim 11 wherein said alloys are solution heat treated for from 5 minutes to 48 hours.

14. A process according to claim 13 wherein said a1- loys are quenched to substantially room temperature following solution heat treatment.

15. A process according to claim 14 wherein said magnesium, zinc and copper components are substantially retained in solution following said rapid cooling.

16. A process according to claim 15 wherein said alloy is aged for from 30 minutes to 48 hours.

* fi f 

2. An alloy according to claim 1 wherein said alloy is substantially chromium free.
 3. A wrought aluminum base alloy having improved toughness and high strength consisting essentially of zinc from 4 to 9 percent, magnesium from 1 to 4 percent, copper from 0.5 to 3.5 percent, zirconium from 0.05 to 0.40 percent, boron from 0.01 to 0.05 percent and the balance essentially aluminum, said alloy being in the heat treated and aged condition and having high strength and improved toughness.
 4. An alloy according to claim 3 wherein the zinc is present in an amount from 5 to 6.5 percent.
 5. An alloy according to claim 3 wherein the magnesium is present in an amount from 2 to 3 percent.
 6. An alloy according to claim 3 wherein the zirconium is present in an amount from 0.1 to 0.2 percent.
 7. An alloy according to claim 3 wherein the boron is present in an amount from 0.01 to 0.02 percent.
 8. An alloy according to claim 3 wherein the copper is present in an amount from 1 to 3 percent.
 9. An alloy according to claim 3 containing titanium up to 0.1% max., manganese up to 0.2 percent max., silicon up to 0.4% max., and iron up to 0.5% max.
 10. An alloy according to claim 3 wherein said alloy is substantially chromium free.
 11. A process for providing improved toughness and high strength in a wrought aluminum base alloy consisting essentially of zinc from 4 to 9 percent, magnesium from 1 to 4 percent, zirconium from 0.05 to 0.40 percent, copper from 0.5 to 3.5 percent, boron from 0.01 to 0.05 percent, balance essentially aluminum, which comprises: A. hot rolling said alloy; B. cold rolling said alloy; C. solution heat treating said alloy at a temperature of from 750* to 1,000*F for at least 5 minutes followed by rapid cooling; and D. aging for at least 30 minutes at a temperature of from 200* to 400*F.
 12. A process according to claim 11 wherein said magnesium, zinc and copper components are substantially retained in solution following said rapid cooling.
 13. A process according to claim 11 wherein said alloys are solution heat treated for from 5 minutes to 48 hours.
 14. A process according to claim 13 wherein saId alloys are quenched to substantially room temperature following solution heat treatment.
 15. A process according to claim 14 wherein said magnesium, zinc and copper components are substantially retained in solution following said rapid cooling.
 16. A process according to claim 15 wherein said alloy is aged for from 30 minutes to 48 hours. 